Various types of paper web theading systems are known, see for example German Patent No. 22 41 127, and the referenced U.S. Pats. Nos. 3,127,079 and 4,187,968, Winterholler et al, assigned to the assignee of this application. These, and other paper threading arrangements known in the industry, permit pulling a paper web on which printing is to be effected through the printing machine. The pulling path is determined by the setting of switches which control the path of a pulling element, around selected cylinders, or bypassing selected cylinders. In this manner, the paper web can be pulled through respective printing stations of the printing machine.
It is desirable that the pulling element be formed of an endless pulling cable, sprocket chain, or the like. The pulling force can be quite substantial, and when using a pulling element which has a finite end, a plurality of drive stations are necessary to move the pulling structure through the printing machine. Using an endless pulling element permits placement of only a single drive element in engagement with the endless cable or sprocket chain; otherwise, a single pullling element can move a cable or pulling element of a finite length only along a single path, by pulling or pushing the respective element.
It has previously been proposed to utilize a threading structure with a finite pulling element in form of a cable, in which the paper web is first secured to the pulling element and the cable is then engaged with motor. The cable is passed between two drums, one paying out cable and the other winding it up; this arrangement again requires two drive elements (see, for example, U.S. Pat. No. 3,127,079).